The present invention relates to a polishing head in a wafer polishing apparatus used in the chemical machine polishing (CMP) of wafers.
Among conventional wafer polishing apparatus comprising polishing heads with retainer rings, there are, for example, those having the structure shown in FIG. 3. This wafer polishing device 1 comprises a polishing pad 2 which is rotated horizontally, and a polishing head 3 which conveys a wafer W by suction and presses the wafer W against said polishing pad 2 from above while horizontally rotating it.
The polishing head 3 comprises a carrier head 4 which is provided so as to be capable of horizontal rotation and moved up-down and left-right by a drive mechanism that is not shown, a wafer holding portion 5 attached to the carrier head 4 so as to be capable of moving in an up-down direction, for holding a disc-shaped wafer W with the surface to be polished face down and for applying pressure to the wafer W from above during polishing and an annular retainer ring 6 attached to the carrier head 4 and provided in a radially outward direction of said wafer holding portion 5.
In the drawing, reference number 7 denotes a membrane composed of a rubber membranous material for applying pressure or suction to wafers, reference number 8 denotes a membrane support for supporting the membrane, reference number 9 denotes an inner tube, reference numbers 10 and 11 denote expandable and contractible sealing means and reference numbers 12, 13 and 14 denote air pressure ducts.
At the polishing head 3 constructed in this way, air pressure fed through the duct 12 causes the first compression chamber 15 to expand to press the retainer ring 6 against the polishing pad 2. Additionally, by supplying a negative pressure through the duct 13, the second compression chamber 16 is made to contract, thus drawing the wafer W up against the wafer holding portion 5, whereas a supply of positive pressure causes the second compression chamber 16 to expand so as to press the wafer W against the polishing pad 2. Furthermore, by supplying air pressure to the duct 14, the inner tube 9 is made to expand, thus pressing the wafer holding portion 5 downward along with the wafer W.
Thus, by adjusting the air pressure supplied to these ducts 12, 13 and 14, the retainer ring 6 is capable of moving up and down independent of the wafer holding portion 5, so that pressure applied from above when polishing the wafer W will press the frictional surface 6a on its bottom end against the polishing pad 2. That is, the retainer ring 6 is brought into contact with the polishing pad 2 when polishing the wafer W, thereby sealing off the space in the radial outward direction of the wafer W and preventing the wafer W from flying out in a radial outward direction.
Additionally, if pressure is further applied to the retainer ring 6 while polishing a wafer W, the reaction from the polishing pad 2 will cause the surface of the polishing pad 2 inside the retainer ring 6 to bulge in a so-called rebound effect. Then, by adjusting the pressure applied to the retainer ring 6 by making use of this rebound effect, the state of polish of the wafer W can be changed actively. That is, the retainer ring 6 also functions as means for adjusting the state of polish of the wafer W.
As shown in FIG. 3, the retainer ring 6 which has these functions has a two-layer structure comprising a steel attachment plate 17 affixed to the carrier head 4, and a frictional layer 18 composed of PPS resin (polyphenylene sulfide resin) affixed to the attachment plate 17 by arbitrary attachment means such as a screw or adhesive which is not shown.
In one aspect, the invention is directed to a retainer ring for a polishing head of a wafer polishing apparatus. The retaining ring has an attachment plate to be affixed to the polishing head, a ceramic friction ring to be brought into contact with a polishing pad, and a resin spacer provided between the attachment plate and the friction ring.
Implementations of the invention may include one or more of the following. The friction ring and the spacer may be respectively formed into an annular shape and positioned adjacent to each other in an axial direction. The spacer may include a covering portion formed on the inner circumferential portion of the spacer. The covering portion may extend along the axial direction in the direction of the friction ring to cover an inner circumferential surface of the friction ring. The inner circumferential edge on a spacer side of the friction ring may be formed in a tapered shape, and the covering portion of the spacer may be formed into a shape that complements the tapered shape. An inner diameter of the spacer may be smaller than an inner diameter of the friction ring. The covering portion of the spacer may have a tip at a position which is set back from a surface of said friction ring which is brought into contact with the polishing pad. A step difference between the tip of the covering portion and the surface of the friction ring may be smaller than a thickness of a circumferential edge of a wafer held by the polishing head. The friction ring may be composed of ceramic SiC, and the retainer ring may be composed of Delrin(copyright).
In another aspect, the invention is directed to a polishing head for chemical mechanical polishing. The polishing head has a wafer mounting surface and a retainer ring provided around the periphery of a wafer on the wafer mounting surface for suppressing movement of said wafer in the radial direction during polishing. The retainer ring includes an attachment plate to be affixed to the polishing head, a ceramic friction ring to be brought into contact with a polishing pad, and a resin spacer provided between the attachment plate and the friction ring.
In another aspect, the invention is directed to a chemical mechanical polishing apparatus. The apparatus has a polishing surface and a polishing head to hold a wafer against the polishing surface. The polishing head includes a wafer mounting surface and a retainer ring provided around the periphery of a wafer on the wafer mounting surface for suppressing movement of said wafer in the radial direction during polishing. The retainer ring includes an attachment plate to be affixed to the polishing head, a ceramic friction ring to be brought into contact with the polishing pad, and a resin spacer provided between the attachment plate and the friction ring.
Possible advantages of the invention may include one or more the following. Microscratches on the surface of a wafer being polished may be reduced. The lifetime of the retaining ring may be increased, and number of preservation or refurbishing steps for the retaining ring may be reduced.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.